Zone Plates

Zone plates are patterns of alternating opaque and transparent regions, called zones, which are used to focus light, much like a lens. However, unlike a lens, which uses refraction to manipulate the light, a zone plates uses diffraction. The incoming light spreads out from each of the transparent regions and creates an interference pattern which creates an image at the focal point. They are also being heavily investigated, because unlike lenses, zone plates can also focus electromagnetic radiation that is not visible, such as x-rays.

Possible Projects: Investigate the properties of different shaped zones. Usually most of the zones are arranged in a circular pattern, but I could investigate the properties of zones plates whose zones are different shapes such as linear, elliptical, and hyperbolic zone plates. Investigate zone plates, which cause a destructive interference pattern at the focal point.

Gradient Refractive Index

A material that has gradient refractive index, just as the name suggests, has a gradually varying refractive index. A gradient refractive index causes light to bend, which is how a mirage works in a desert, where the gradient refractive index is caused by the differences in the refractive indexes of the hot air and the denser cool air below it. This concept is also used in making fiber optic cables. The gradient refractive index in the cable, keeps the light from leaving the cable and keeps it moving forward. Furthermore, this concept can be used to create lenses, by simply controlling the diffusion of ions which cause the refractive index to vary, as opposed to shaping a piece of glass to create a conventional lens.

Possible Projects: Investigate using a gradient refractive index to make tunable lenses by changing the distribution of ions, or using sound to manipulate a refractive liquid.

Bessel Beams

A Bessel beam is radiation that is described by the Bessel function of the first kind. A perfect Bessel beam does not diffract, and is self healing. This means that a Bessel beam, unlike normal light, does not spread out. Also because it is self healing, a Bessel beam reforms, when impeded somewhere down the beam's axis. However, in order to create a true Bessel beam, one would require an infinite amount of energy. Usually approximations of the Bessel beam are created by passing a Gaussian beam through an axicon lens.

Possible Projects: Investigate the possibility of creating a tunable lens that can create an approximation of a Bessel beam much like an axicon.

Solar Stirling Engine

A Stirling engine is a heat engine that uses two pistons that cyclicly compress a gas at different temperatures. A Stirling engine focuses light to heat one side of the Stirling engine, causing one part of the engine to be hotter than the other, this causes the gas inside of the engine to expand, thus driving one piston back, and as the gas is cooled once again, it is pushed back by another piston. As the pistons move through their cycle, they turn a wheel, thus converting solar energy into mechanical energy.

Possible Projects: Improve the efficiency of a demonstration model of one of these Stirling engines by testing different methods to focus the sunlight.